1. Field of the Invention
The present invention relates to a technique for generating image data to be output to a printing unit.
2. Description of the Related Art
An anti-counterfeit technique or authenticity determination technique for printed matter includes a printing method of an image which cannot be visually recognized (or is difficult to visually recognize) under ordinary light but can be easily recognized using an apparatus such as an infrared camera sensitive to the infrared light range under infrared light.
As a representative printing method, the following method is known (for example, Japanese Patent No. 3544536). That is, using the fact that of inks of respective color components (i.e., cyan (C), magenta (M), yellow (Y), and black (K)), only black (K) ink has a large infrared absorption characteristic, an image is printed on a printing medium using black (K) for a latent image region and using cyan (C), magenta (M), and yellow (Y), which have a small infrared absorption characteristic, for a background region; output printed matter may then be irradiated with infrared light in order to allow discrimination of an image using an infrared camera.
According to the method described in this document, under infrared light, a portion generated using black (K) becomes dark, and a portion generated using cyan (C), magenta (M), and yellow (Y) becomes bright. In this way, a binary discrimination image configured by bright and dark portions can be made to appear under infrared light.
According to the related art, although a binary discrimination image can be made to appear under infrared light, it is difficult to cause the appearance of a multi-valued discrimination image of three values or more. For this reason, design of a discrimination images to be made to appear suffers large limitations. When this technique is applied to an anti-counterfeit technique of printed matter, a binary discrimination image is likely to be relatively easy to counterfeit.